Distinctive phases and variability of vibration-induced postural reactions highlighted by center of pressure analysis

Abstract

Background The vibration-induced postural reaction paradigm (VIB-PR) offers a unique way for investigating sensorimotor control mechanisms. Measures of VIB-PR are usually calculated from the whole VIB period, yet recent evidence proposed that distinctive mechanisms are likely at play between the early vs. later phases of the postural reaction. Objectives The present work verified if spatiotemporal analyses of center of pressure (COP) displacements can detect differences between these early/later phases of VIB-PR. Also, we further characterized the intra/inter-individual variability of COP measurements, since the underlying variability of VIB-PR remains largely unexplored. Methods Twenty young volunteers realized two experimental conditions of bipodal stance with eyes closed: (i) bilateral VIB of tibialis anterior (TIB) and (ii) Achilles’ (ACH) tendons. Each condition consisted of five trials and lasted 30 s as follows: 10 s baseline, 10 s VIB and 10 s post-VIB. Linear COP variables (antero-posterior (AP) amplitude & velocity) were computed for both VIB and post-VIB periods using the following time-windows: early 2 s, the later 8 s and the whole 10 s duration. Intra- and inter-individual variability were respectively estimated using the standard error of the measurement and the coefficient of variation. Both variability metrics were obtained using five vs. the first three trials. Results Significant contrasts were found between time-windows for both VIB and post-VIB periods. COP variables were generally higher during the early 2 s phase compared to the later 8 s phase for both TIB [mean difference between 8 s– 2 s phases: Amplitude AP = -1.11 ± 1.14 cm during VIB and -2.99 ± 1.31 during post-VIB; Velocity AP = -1.17 ± 0.86 cm/s during VIB and -3.13 ± 1.31 cm/s during post-VIB] and ACH tendons [Amplitude AP = -0.37 ± 0.98 cm during VIB and -3.41 ± 1.20 during post-VIB; Velocity AP = -0.31 ± 0.59 cm/s during VIB and -3.89 ± 1.52 cm/s during post-VIB]. Most within- and between-subject variability scores were below 30% and using three instead of five trials had no impact on variability. VIB-PR patterns were quite similar within a same person, but variable behaviors were observed between individuals during the later phase. Conclusion Our study highlights the relevance of identifying and separately analyzing distinct phases within VIB-PR patterns, as well as characterizing how these patterns vary at the individual level.

Vibration-induced postural reactions: a scoping review on parameters and populations studied

“…Also, Kadri et al found that these patterns varied between and within individuals. The neurophysiological and behavioral correlates of these observations remain unknown (Kadri et al, 2020 , 2023 ), calling for further fundamental work with neurologically and physically healthy individuals. In terms of knowledge gaps, however, our review highlights a greater need for studies testing VIB-PR with other populations than healthy adults.…”

“…Therefore, it might be easier to compare their findings to previous results obtained from the same muscles/tendons. However, different patterns of VIB-PR have been observed when targeting the tibialis anterior tendons vs. the Achilles tendon (Kadri et al, 2023 ), which puts into question why only the Achilles tendons are chosen in most studies. Testing other musculotendinous structures would give a more complete picture of regulatory mechanisms involved in keeping balance in different directions and using different joints.…”

“…Choosing the most appropriate duration, even for other applications such as illusions, remains mostly arbitrary due to lacking empirical data (Seizova-Cajic et al, 2007 ). Recent work suggested that VIB-PR evolves dynamically over time, with at least a first phase of rapid postural reaction (first 2–3 s), followed by a later phase (at least 8 s) where postural control tends to restabilize (Capicíková et al, 2006 ; Duclos et al, 2014 ; Kadri et al, 2020 , 2023 ). We would at least recommend choosing longer durations instead of shorter ones, in order to avoid missing relevant behaviors and underlying mechanisms of control.…”

“…We would at least recommend choosing longer durations instead of shorter ones, in order to avoid missing relevant behaviors and underlying mechanisms of control. In Kadri et al ( 2020 , 2023 ), there were many participants who did not even reach their maximal amplitude of reaction after 10 s of vibration.…”

“…For example, if eliciting tendon reflexes is what the research team is aiming for, short vibration bursts of 0.03 s have been shown to be sufficient (dos Santos Fornari and Kohn, 2008 ). On the other hand, if a research team aims to describe the time course of CoP displacement, induce lasting neuroplastic changes or investigate sensory-reweighting mechanisms necessary for reaching postural re-stabilization when a sensory source is no longer recognized as appropriate (Kadri et al, 2020 , 2023 ), a longer vibration duration such as >10 s should be considered.…”